BREAKING: fs.read() & fs.write() should return objects

[RyanZim]

For forward-compat with util.promisify()

Resolves #436

Needs docs yet

[coveralls]

Coverage increased (+0.2%) to 87.174% when pulling d3545d4 on read-write-obj into 15db64f on master.

[RyanZim]

Windows CI fails due to funky windows timestamps; unrelated to this change.

[coveralls]

Coverage increased (+0.2%) to 87.174% when pulling 5a8d568 on read-write-obj into 15db64f on master.

[ghost]

@RyanZim But why does the node.js v4 build pass and the v6 build fail?

[RyanZim]

@Yamboy1 It's a 32-bit windows issue; nothing critical.

[ghost]

@RyanZim It's reasons like this why I prefer to use Linux

[ghost]

Windows just has too many bugs